The present invention relates to a scarifier tooth assembly for use on motor grader for digging furrows in the ground. Such teeth are secured to the ripper bar of the grader by a plurality of elongated shanks. The shanks commonly used for this purpose are substantially "J"-shaped with the upper ends thereof being secured to the ripper bar and the lower ends each define a flat bearing surface against which the tooth is held and a pair of parallel locking grooves in the side walls thereof which are angularly disposed with respect to the bearing surface. The teeth used with such shanks are of integral construction having a forward tapered point or digging portion extending from an inverted "U"-shaped rear clamping portion. The clamping portion of the teeth defines a flat interior bearing surface which is adapted to abut the bearing surface on the shank and a pair of inwardly projecting lateral flanges which are slighted into the locking grooves in the lower portion of the shank. By forcing the tooth onto the shank, the flanges on the teeth are held within the locking grooves and the flat bearing surface on the underside of the clamp portion of the tooth is wedged against the bearing surface on the shank thereby securing the tooth to the lower portion of the shank.
While the aforesaid tooth construction is in wide-spread use, there are several problems inherent in its construction. First, the point or digging portion of such teeth wear out relatively rapidly. With this integral tooth-clamp construction, replacement of the point portion necessarily requires replacement of the clamp portion as well thereby increasing the cost of point replacement.
Secondly, this integral construction is difficult and expensive to fabricate. It should be forged and not cast due to the strength requirements and forging this tooth with the channels therein defined by the inwardly directed flanges is a difficult and expensive operation. Further, the point and clamping portions of the tooth have to be separately heat-treated to different degrees of hardness. The point which is the digging portion of the tooth must be hard to prevent wearing and withstand the forces generated during the digging operation. The rear portion of the tooth must be more ductile to withstand the clamping action. Separate heat-treating operations conducted on an element of integral construction again increase the cost of manufacture.
Thirdly, when the tooth is subjected to substantial vertical forces, a large portion of those forces are born by the softer flanges which extend into the locking grooves of the shank. These forces often result in a shearing of the flange, destroying the entire tooth.
Fourthly, the bearing surfaces on the shank and the underside of the clamping portion of the tooth which are wedged together are flat as are the walls forming the parallel locking grooves in the shank. While these flat surfaces are designed to prevent any lateral movement between the tooth and shank, inconsistencies in construction often result in an imperfect fit. As a result, either an improper fitment or no fitment at all is obtained which can require replacement of the entire assembly or result in breakage of the tooth.
The combination of each of the aforesaid shortcomings results in a short life and high replacement costs for scarifier teeth. It would therefore be desirable to provide a scarifier tooth assembly which is compatible with these conventional shanks yet which would allow for replacement of the point without the need to replace the clamp portion of the tooth, which would reduce the overall cost of manufacture both in the forging and heat-treating stages, which would accommodate inconsistencies in the locking grooves of the shank and which would still provide a rigid securement of the tooth to the shank in a manner so as not to subject portions thereof to inordinate shearing forces. The tooth assembly disclosed and claimed herein attains these objectives.